Solar System for Small Off-Grid Bathroom.

[Crunchiness]

Hi, new guy here looking to develop a small solar setup for an off-grid bathroom.

Goal: Have a low-maintenance system to power the following items of an off-grid bathroom used in some backcountry skiing operations:
There will be a generator available ( 25kw genset) for approximately 2-3 hrs every couple of days, but due to the nature of the operation we would like to keep the bathroom running all the time ( Users need a bio-break at any time)


-2 Propane interaction toilets - 12v (using a 120 to 12v adapter) @ 1.3a per "flush" for 15min each - Expect a total of 6 flushes a day - 24wh/day
-12 ea 15w lights - run for 8hrs run time per day - 960wh/day (guests leave the lights on)
-Small propane water heater- 400wh/day
-Small water pump- 400wh/day
1.384 kwh/day - x 1.20 for passive loads - 2051wh/d

Therefore I`m planning on a 4800 kWh system to provide two days of runtime.
These are calculated using worst-case scenarios.

These are the products I`m looking at right now:
48v inverter
2 x 24v LiPo4 BATTERY

We already have 4 of these panels from a recycled radio repeater: Panel

The questions I have:

- I need to run a 100ft wire from the panels to the inverter to get them in a good spot (max sun). The above inverter has a Built-in MPPT - This will allow me to run the panels in a series to minimize the need for a heavy gauge wire to the panel- Correct?
My calculations show that an 8AWG cable will allow for less than 3% voltage drop. Does this feel right?
(I'm using a 1.25 factor due to cold weather on MPV and MPP (Conservative) )

-The batteries are self-heated, but should only be used in case of a failure of the propane heating system for the bathroom. How reliable is this system? Are there self-heating batteries at a similar pricepoint elsewhere? Not savvy to all the good sites to look for things.

-These are 24v Batteries. I`m planning on wiring in a series to jump to 48v. The manual says this is possible... anything seem like it wouldn't work by doing this?

-The budget is $4000. I figure I`m probably going to spend $1500 on conduit/assorted wiring/connectors/etc. That leaves me around $500 more to spend... anything else I should consider for a setup like this at that price point?

Thanks! I've used to residential electrical and heavy electrical, but this small-scale solar is head-scratching at times.

 

[timselectric]

These are the products I`m looking at right now:
48v inverter
2 x 24v LiPo4 BATTERY

We don't recommend putting BMS controlled batteries in series. Get a 48v battery, if you want a 48v system.
Unless you want the additional maintenance of balancing the batteries every few months.
Or more often, if the battery heating gets used.

 

[Rednecktek]

-2 Propane interaction toilets - 12v (using a 120 to 12v adapter) @ 1.3a per "flush" for 15min each - Expect a total of 6 flushes a day - 24wh/day

Is that 1.3a on the 120v side or the battery side?

-Small propane water heater- 400wh/day

Is that one of those small camping shower on demand heaters? Or something that has a power jack?

1.384 kwh/day - x 1.20 for passive loads - 2051wh/d

What's your maximum All-The-Things-Run-At-Once load? Everything I'm seeing says a 48v system is overkill and you would be able to run everything off a 12v system with Maybe a small inverter if there's anything in there that requires 120v. The toilet for example uses a 12v power supply so you can save a little complexity and efficiency by running a 12v system and taking that wall wart out of the loop. Likewise with the water pump and lights, there's no reason you couldn't run 12v versions of that.

So you're looking at about 200Ah per day on 12v rounding up, 400 a day for a couple extra days.

2 x 24v LiPo4 BATTERY

What about just running a 24v system and a step-down for the 12v stuff?

You'll want batteries that have heaters because of the cold. Trophy is about the only company that sells heated rack mount batteries, but many smaller brands have heated 12v batteries. Might be something to consider.

 

[BryceFreeman]

-These are 24v Batteries. I`m planning on wiring in a series to jump to 48v. The manual says this is possible... anything seem like it wouldn't work by doing this?

Connecting the batteries to make a 48v battery bank will need extra maintenance of balancing them every few months. Get a 48v battery will be better if you don't want that. You can get more of them in parallel to get more capacity.

- I need to run a 100ft wire from the panels to the inverter to get them in a good spot (max sun). The above inverter has a Built-in MPPT - This will allow me to run the panels in a series to minimize the need for a heavy gauge wire to the panel- Correct?

Yeah I think so. To set your solar panels at the max voc of the hybrid inverter is the best way to make it work.

 

[Crunchiness]

Is that 1.3a on the 120v side or the battery side?

Taken from the a Killawatt meter

Is that one of those small camping shower on demand heaters? Or something that has a power jack?

On-demand heater with 120v outlet.

What's your maximum All-The-Things-Run-At-Once load? Everything I'm seeing says a 48v system is overkill and you would be able to run everything off a 12v system with Maybe a small inverter if there's anything in there that requires 120v. The toilet for example uses a 12v power supply so you can save a little complexity and efficiency by running a 12v system and taking that wall wart out of the loop. Likewise with the water pump and lights, there's no reason you couldn't run 12v versions of that.

So you're looking at about 200Ah per day on 12v rounding up, 400 a day for a couple extra days.

Hmmm I totally would, I but I feel it would be easier to tie this into the genset with a 120v system (easily place a service selection switch between inverter AC output and the system) . Unless there's no real benefit to doing that.

What about just running a 24v system and a step-down for the 12v stuff?

You'll want batteries that have heaters because of the cold. Trophy is about the only company that sells heated rack mount batteries, but many smaller brands have heated 12v batteries. Might be something to consider.

Good to know. I`ll check them out.

 

[Crunchiness]

We don't recommend putting BMS controlled batteries in series. Get a 48v battery, if you want a 48v system.
Unless you want the additional maintenance of balancing the batteries every few months.
Or more often, if the battery heating gets used.

Okay noted. I`ll check into the trophy 48v system.